Help please!

[79C10Shorty]

79C10Shorty


Ok, not super familiar with boats but I am very confortable working on lots of other complicated equipment as well as good around a v8 Chevy .

So I bought a pretty little 19 foot sunbird with a1995 mariner 150 on it. Put it in the water and ran for a day. Great fun, it never missed a beat. One thing was it is a little hard on gas, harder than I anticipated. It is really fast, faster than I want to go! And it was lazy getting on plane. Original owner said he ruined the original prop, and put on an odd donor prop. He never thought to keep the original prop either to see what it was.
So I call up the marine store and explain, also, I have no tack. Boat shop says difficult but let's try a 15 pitch, four blade that is if I remember correctly about 14" in diameter. ( I may not have the correct size mentioned but the new prop is the maximum tolerable diameter for the engine. A larger one simply would not fit).
The old donor prop, just removed, was a 20 pitch four blade but one and a half inches smaller than the shiny new prop.
Hope you are still with me.
So while I was at the marine store I also bought a water pump kit, since I did not know the last date of replacement.
Now I removed the lower unit, installed the pump, reinstalled the lower unit all in an evening and all seemed to go easy. Even shift linkage slid together well. This was my first time ever seeing one apart.
I put-the boat on forward, manually I can spin the prop one way and compression the other. Then I put the boat in reverse and just the opposite, as I expected from the prop. Perfect.
I connect the garden hose to the motor, get the water running and hit the key.
It starts first click and sounds good. No much water coming from the pee hole so I pull a line off the motor briefly and its pumping good. Ready to go boating!
Me and the wife load up and head to the boat launch. Get the boat in and all set, I leave at just minimum throttle. Already I notice how fast I am going at virtually no throttle. I cruise for a minute to deep water and drop the hammer.
I should be planing well at this point but you guessed it. Trouble .
The motor revved just as if there were no prop at all. I slam off to neutral immediately. Going again at no throttle working well. Same thing happens when I try again.
Disgusted , I quickly put the boat I the trailer without taking good time to troubleshoot . I dropped it of at the marine store where it sat for two weeks where they were swamped with work.
I just brought it home today to try and figure it out.
My main concern is damaging the engine.
What do you think? Is this a prop issue or something happened when I dropped the lower unit and the prop is fine .
I will add that the lower unit came off and on very easy. I did it myself so no liting device so there was no overforce of anything, all bolts turned well and mechanically all appeared to be in order .
I did this procedure with the boat in neutral.

Thanks for any advice

 

[Sea Rider]

Welcome to Iboats,

Receiving a donor prop is he worst you can do, won't know if over or under pitched for your particular combo use. Go for a prop that revs at full wot revs as currently loaded. Once there can throttle at the rpm/speed range of your prefference. If that's a 2 strokes OB expect a fuel comsumption per hour of at least 12% of your HP at full hammer down....who said boating was cheap LOL!!

Happy Boating

 

[79C10Shorty]

The thing is I'm not looking for speed. Just at s plane is the fastest I would normally ever go.
Do you think my issue sounds prop related or something worse?

Thanks

 

[Chris1956]

A 150HP motor on 19 foot Sunbird will give good performance. If she is hard to plane with that 20" pitch prop, the prop pitch is likely too much, However, dropping to 15" in pitch is too low a pitch.

I would expect a 17" pitch prop to give you about what you want.

As for your new prop issue, it sounds like the prop hub is defective. Is it one of those modular prop hubs, or a pressed in hub? Does it have the correct thrust washer, splined washer and spider washer?

 

[NHGuy]

What kind of engine is this. There is a chance the lower isn't transferring power correctly. Perhaps it didn't go back together right after the service you did.
You could stick the donor prop back on for a try, to see if the old condition returns.
But as I say, something could be out of whack.

 

[79C10Shorty]

Ok.
Finally managed to get it back in the water with the old donor prop. It worked just like it did before with the donor prop. So no more revving ans spinning.
I did take careful attention to detail when removing the new prop from the boat. There was no sign of a spin hub. The hub looked just like brand new and the witness marks from the spline lock nut says that it never spun on the prop. I really can't see how that would happen anyway with that set up.
The new prop is a hustler 13.5 x 15 that is put together with a hub kit. Very nice looking equipment .
So that leaves me with wondering where to go next. I can return the prop for an exchange.
As mentioned here I should try a 17 pitch. Should I stay with the 13.5 diameter?
The donor prop is much smaller. The 13.5 is the largest that will fit on the motor.

Thank you so much for all the valuable advice.

 

[batman99]

For your 19 foot sunbird with a 1995 mariner 150 HP", try:
- 4 blade 15" - if heavy loaded.
- 4 blade 17" - if medium weight loaded.

I use these 4 blades on my 1985 OMC 115 and it loves them much better an 3 blades. Especially when out of the hole - where blade traction does matter.

Since each motor / boat combo is unique, try the 15" pitch and compare against WOT RPMs. If over revving at average loaded WOT, then try 17" blade next. When it comes to prop sizing, "not one size fits all".

 

[Sea Rider]

Don't see a word about RPM achieved with each individual prop test. If don't count with a tach installed on console or even an induction tach on OB will never dial best prop performer, all will be wild guesses. Props, rpm and tachs works hand in hand as you will discover, the sooner the better for your OB.

Happy Boating

 

[79C10Shorty]

Ok.
There is a tach on the boat but for some reason when there is power to it , it just moves up to 1000 and stays there . I will get a new one and connect it before I change the prop.
What does WOT stand for? Sorry for the ignorance.

Thanks

 

[batman99]

WOT = Wide Open Throttle. For your "1995 mariner 150 HP" engine, max RPM is probably between 5,500 to 6,000 RPM. If you provide your engine's SN, the Mariner engine folks can confirm exact MAX RPM of you specific model of engine.

RPM gauges can be bought from iboats store. Do double check hole size and max RPM range before buying. re: Some RPM gauges go up to 5,000 and others go up to 7,000 RPM. re: http://www.iboats.com/Boat-Tachometers/dm/cart_id.304579701--session_id.735598742--view_id.248010

 

[79C10Shorty]

I have yet to get my boat home to work on the tach issue.
I have just been curious about something through all this. I am learning now what pitch is to a prop but what significance is the diameter ? Is there a such thing as to much diameter. What would the comparison be between two 17 pitch props , one large like 13.5 and one that is like 12".

Thanks

 

[Chris1956]

normally you will choose a prop by it's style and it's pitch. The prop diameter is usually prechosen by the manufacturer to work with that pitch. For example, prop sizes (diameter, pitch) usually change together, say 12 3/4" X 19P; 12 1/2" X 21P and 12 1/4 X 23P

 

[79C10Shorty]

Ok, makes sense. The marine store suggested I drop to a 15 pitch. Makes sense that it just clears the prop all around.
So I can expect that if I order a 17 pitch prop it will defiantly get smaller.

Thank you